Unauthorized tampering into the inside of a package, such as intrusion into a housing having multiple circuit cards, or intrusion into a container having a protected volume of items is an ever present problem. Various measures are taken to prevent, or detect such intrusion and provide an external alarm of the intrusion, or undertake other protective actions. Anti-tamper devices, including the deliberate destruction of a device when a tamper has been detected, are known in field of tamper identification.
As an example, a door of a house may include a sensor for detecting motion and activating an alarm when motion of the door is detected. Another example may be a wiring mesh that is placed in a top layer of a multiple layered circuit card. When the wiring mesh is cut, because someone is cutting into the layers of the circuit card in an attempt to reverse engineer the circuit card, a voltage may be interrupted in the wiring mesh which may activate a current to destroy any logic in the circuit card.
Another example is disclosed in U.S. Pat. No. 7,495,555, issued Feb. 24, 2009, which includes a method for detecting and reporting magnetic fields in the proximity of a utility meter in order to report tampering of such a meter. Utility meters may be adversely affected by spurious electromagnetic energy placed adjacent to a utility meter. If such energy is strong enough, the energy may reduce or eliminate altogether the meter's ability to measure the consumed energy. In order to combat this problem, several magnetic sensors may be placed inside a utility meter, where each sensor may have a different threshold setting. If a magnetic field is applied externally to the utility meter by a customer and the field is strong enough, a combination of the sensors may detect the external electromagnetic energy. The event may be reported by each magnetic sensor to a centralized computer which, in turn, may report the event to a transmitter residing within the utility meter for remote communication.
The present invention, as will be explained, detects tampering into a container, such as a housing of circuit cards, but does not use a central point, such as a computer, to collect the report of the tampering event from each independent sensor. Instead, the present invention propagates the tampering event to other sensors that are positioned in spatial sequence to the initial sensor that detected the tampering event. In this fashion, each of the sensors is alerted of the tampering event in a cascade manner, or in a sequential manner. In addition, the present invention advantageously reports the tampering event from one sensor to an adjacent sensor without need of physical connections between one sensor and an adjacent sensor.